In the dental clinical field, as a method for evaluating the presence of dental plaque attached to the surface of a tooth and the state of the dental plaque, dentists have primarily conducted visual inspection up until the present.
Since the color of dental plaque is white or translucent white, which is the same color as that of the surface of a tooth, it is difficult to recognize the attachment of the dental plaque on the surface of the tooth. In dental clinical practice, a dental plaque coloring method has been conventionally used. The dental plaque coloring method is a method using a plaque coloring solution, and in dental medical practice under insurance in Japan, Plaque Control Record (PCR method) developed by O'Leary has been introduced. With the PCR method, a tooth surface is divided into four portions, and the ratio of the number of portions to which dental plaque is attached to the total number of tooth surfaces is determined for evaluation of the state of oral cleanliness. The method is, however, a two-level evaluation method that simply evaluates presence or absence and hence fails to provide details of the state of dental plaque attachment. Further, the dental plaque coloring operation itself gives a patient strong discomfort, and removal of the coloring solution after the coloring operation is cumbersome.
Moreover, since portions other than dental plaque are also colored, the inspection method undesirably has low specificity and many other disadvantages. It cannot therefore be said that the PCR method is adequate to spread the recognition of the importance of oral cleaning.
As a method for evaluating dental plaque removal effects provided by a variety of brushing methods and motorized toothbrushes, the Loe-Silness dental plaque index is known. The method does not rely on coloring and cannot therefore clearly show the boundary among dental plaque, a tooth, and a periodontal tissue. The method provides the following four-level evaluation results: no dental plaque attachment; tactually recognized dental plaque; visually recognized dental plaque; and a large amount of dental plaque attachment. It cannot, however, be said that the method is a quantitative evaluation method because there are large differences among the four levels.
The dental plaque evaluation method among dental health evaluation methods provides scored results for seeming digitization and hence objectivity. The method, however, has problems of poor reproducibility and lack of true objectivity, that is, multiple inspection operators who execute the method cannot provide consistent values. It cannot therefore be said that the method is widely used in dental clinical practice. As an evaluation method based on dental plaque coloring, there is a known method described in PTL 1. The method is executed as follows: toothpaste to which 0.01 to 2.0 weight % of fluorescent dye is added is used to attach the fluorescent dye to dental plaque at a time of tooth brushing; light from an incandescent lamp or a fluorescent lamp is applied through an appropriate filter to the fluorescent dye to emit light from the fluorescent dye; and the amount of dental plaque is detected based on the amount of the emitted light.
PTL 2 also discloses a dental plaque coloring method. The method, however, has problems of bitterness of the coloring agent and low stability of the coloring agent when the coloring agent is stored. PTL 3 discloses a method using both a dye and light. The method is based in principle on the fact that the dye is excited by the light and emits fluorescent light, but the dye itself needs to strongly adhere to the dental plaque. Fluorescent dyes, such as chlorophyll and fluorescein, cannot also sufficiently dye dental plaque. Further, PTL 4 discloses a method for detecting dental plaque only by using specific light. The method, however, has a problem of inability to detect dental plaque formed in an initial stage.
In recent years, studies of methods for quantitatively evaluating dental plaque have advanced. For example, NPL 1 discloses a method for capturing an oral cavity photograph after dental plaque coloring in the form of a digital image and computationally calculating the area of the dental plaque in comparison with the surface of the tooth. The method, however, has difficulty in distinguishing the dental plaque from gingiva. Since an optical photograph captures an object only in a planar manner, front and rear sites in the photograph are likely to be evaluated differently. A dental plaque detection method based on a quantitative light-fluorescence method (QLF method: Quantitative light-fluorescence method) using light of a specific wavelength (370±40 nm) allows more characteristic visualization of dental plaque than surrounding tissues. The method therefore eliminates the need of dental plaque coloring, but captures the dental plaque only in a planar manner as in a typical optical photograph. In reality, no image processing software based on a typical optical photograph or an optical photograph using a specific wavelength has been brought into practice, and it can hardly be said that development of the image processing software is underway.
NPL 2 discloses a method for collecting impressions of dental plaque before and after removal thereof, performing digital three-dimensional scanning on a plaster cast of the tooth before and after the removal of the dental plaque, and stereoscopically evaluating the attachment of the dental plaque. The collection of impressions twice, i.e., before and after the removal of the dental plaque is, however, cumbersome, and practicability of the method is therefore very low in the clinical field. Further, the dental plaque measurement and evaluation based on the plaster cast is not realistic.
In recent years, an OCT apparatus for dental purposes has been developed and used to diagnose dental caries (PTL 5). PTL 5, however, only describes a method for measuring dental caries.
On the other hand, no noninvasive quantification of gingiva or alveolar bone has been reported.